From 588c243929bb899e2520a1220cc9136dab2e0271 Mon Sep 17 00:00:00 2001
From: Siegfried Pammer <siegfriedpammer@gmail.com>
Date: Sun, 2 Nov 2025 11:47:10 +0100
Subject: [PATCH] #3593: ObjectInitializers: allow castclass instructions
 wrapping the init instruction to support the pattern used for covariant
 returns on non-supporting platforms such as .NET 4.x.

---
 .../TestCases/Pretty/InitializerTests.cs      | 19 +++++++++++++++++++
 ...ransformCollectionAndObjectInitializers.cs | 11 +++++++++++
 2 files changed, 30 insertions(+)

diff --git a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/InitializerTests.cs b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/InitializerTests.cs
index bad7cbccd..02f377974 100644
--- a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/InitializerTests.cs
+++ b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/InitializerTests.cs
@@ -229,6 +229,11 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty.InitializerTests
 			public string S = "abc";
 			public Item I;
 		}
+
+		public record DerivedFields : Fields
+		{
+			public ConsoleKey E;
+		}
 #endif
 
 		public interface IData
@@ -1145,6 +1150,20 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty.InitializerTests
 				}
 			};
 		}
+
+		public DerivedFields DerivedRecordTest(DerivedFields input)
+		{
+			return input with {
+				A = 42,
+				D = 43,
+				I = new Item {
+					Value7 = input with {
+						A = 44,
+						D = 45
+					}
+				}
+			};
+		}
 #endif
 
 		private TData GenericObjectInitializer<TData>() where TData : IData, new()
diff --git a/ICSharpCode.Decompiler/IL/Transforms/TransformCollectionAndObjectInitializers.cs b/ICSharpCode.Decompiler/IL/Transforms/TransformCollectionAndObjectInitializers.cs
index b3d90d935..68c028776 100644
--- a/ICSharpCode.Decompiler/IL/Transforms/TransformCollectionAndObjectInitializers.cs
+++ b/ICSharpCode.Decompiler/IL/Transforms/TransformCollectionAndObjectInitializers.cs
@@ -47,6 +47,13 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			var insertionPos = initInst.ChildIndex;
 			var siblings = initInst.Parent!.Children;
 			IMethod currentMethod = context.Function.Method!;
+			// we allow a castclass instruction to wrap the init instruction:
+			// this is needed, for example, for inherited record types used on .NET runtimes (e.g., .NET 4.x),
+			// where covariant return types are not supported.
+			if (initInst.MatchCastClass(out var arg, out var targetType))
+			{
+				initInst = arg;
+			}
 			switch (initInst)
 			{
 				case NewObj newObjInst:
@@ -100,6 +107,10 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					}
 					return;
 			}
+			if (targetType != null)
+			{
+				instType = targetType;
+			}
 			// Copy-propagate stack slot holding an 'ldloca' of the variable
 			if (pos < block.Instructions.Count && block.Instructions[pos + 1] is StLoc { Variable: { Kind: VariableKind.StackSlot, IsSingleDefinition: true }, Value: LdLoca ldLoca } stLocStack && ldLoca.Variable == v)
 			{